Fix V3Table trying to generate 'x' bits in the lookup table. (#5491)

Due to out of range selects, V3Table attempted to create a table in the
constant pool with an 'x' value in it, which caused an internal error.

Ensure V3Table behaves the same for out of range selects as the original
logic would.

There is a related bug #5490, about leaving partially out of range
selects in the logic after inserting bounds checks in V3Unknown.

src/V3Table.cpp

@@ -315,6 +315,7 @@ private:
             for (TableOutputVar& tov : m_outVarps) {
                 if (V3Number* const outnump = simvis.fetchOutNumberNull(tov.varScopep())) {
                     UINFO(8, "   Output " << tov.name() << " = " << *outnump << endl);
+                    UASSERT_OBJ(!outnump->isAnyXZ(), outnump, "Table should not contain X/Z");
                     outputAssignedMask.setBit(tov.ord(), 1);  // Mark output as assigned
                     tov.addValue(inValue, *outnump);
                 } else {